The invention relates generally to the field of tone and volume control circuits for audio frequency entertainment devices and more particularly to an improved single control power-frequency circuit which is especially adaptable for use in controlling an audio electrical signal in automotive radios and tape players.
In entertainment devices, such as radios and tape players, it is desirable to provide a minimum number of tuning controls which enable the operator to simply adjust the device to obtain a desired mode of operation.
Separate tuning controls for controlling the volume and tone quality of audio signals are usually provided. These controls generally comprise continuously variable potentiometers which function independently of one another. In addition, many entertainment devices provide an additional control for emphasizing either the high or low ends of the frequency spectrum of the resultant audio signal produced by the entertainment device. This additional control is commonly referred to as a "booster" circuit. These booster circuits provide for the selective emphasizing of certain frequency ranges of the audio signal while maintaining the magnitude of the audio signal substantially constant in the unemphasized frequency ranges. To accomplish this frequency boost, prior art circuits use complex and costly tuning circuits, many of which use expensive multitaped potentiometers.
These prior art booster circuits ignore the fact that the reason a booster circuit is actuated by the operator of an entertainment device is to increase the dynamic brilliance of the sound coming from the device. Thus in practice, the operator of a radio first actuates his prior art booster circuit and then adjusts the volume control of the radio to obtain a larger magnitude audio signal throughout the entire audio frequency range. These separate tuning operations produce the dynamic brilliance of the audio sound which the operator desires. Prior art circuits go to extreme lengths to prevent any overall increase in the audio level whenever a frequency booster circuit is actuated. Thus two tuning operations are always required.
Such additional tuning operations are particularly annoying to the operator of a motor vehicle who is trying to adjust the tuning of his car radio while driving. An operator of a motor vehicle requires simplified tuning controls which will rapidly enable him to obtain a desired mode of operation from the audio frequency entertainment devices located within his motor vehicle. This requirement is primarily responsible for the development of pushbutton automobile radios. However automotive tone control devices have not recognized the fact that when the operator desires to emphasize either the base or treble ranges of his audio frequency device, he invariably also desires an overall increase in the loudness of the audio signal throughout the entire audio frequency range.